This invention relates to a toner for developing a static image to be used for a copying machine or a printer, a method producing the toner, and an image forming method using the toner.
Recently, a digital image formation system become to the main current in image forming method by electron-microscopic photography. The image forming method by the digital system is based on the technique to make appear a small dot image of pixel having a size such as 1200 dpi, number of dot per inch, so a high quality image technique to reproduce the small dot with a high fidelity is required. The minimization of the toner particle diameter is proceeded from such the viewpoint.
A polymerized toner produced by a suspension polymerization or an emulsion polymerization has been noticed as a means for making small the toner particle diameter and for unifying the size distribution and the shape of the toner particles. Japanese Patent Publication Open to Public Inspection, hereinafter referred to as JP O.P.I., No. 2000-214629 discloses that the toner produced by the polymerization method can be controlled in the shape, roundness and the size distribution thereof.
A heat-roller fixing method is widely applied as a method for fixing a toner image formed on an image forming support such a sheet of paper by which the image forming support on which a toner image is formed is passed between a heating roller and a pressure roller to fix the toner image. The heat-roller method has a drawback such that an image contamination tends to be occurred by an off-set phenomenon which is caused by adhesion of the melted toner onto the heating roller.
It has been known as a means for prevent the occurrence of the off-set phenomenon that the heating roller of the fixing device is coated with silicone oil to give a mold-releasing ability to the roller. This method is advantageous since there is no limitation on the kind of the toner. However, the method is not suitable for business use because writing by a ball-point pen on the support paper is made difficult by adhesion of the silicone oil on the paper. In the market, the copied document is directly used as a business document and the writing on the document is usually required. Accordingly, the method of silicone coating is becoming one not satisfying the requirement at the present time.
For responding to such the requirement, a technique is applied by which a mold-releasing agent such as a wax is added into the toner itself for providing the mold-releasing ability. JP O.P.I. No. 3-296067 discloses a toner in which polypropylene as the mold-releasing agent is dispersed in the binder polymer to form a domain-matrix structure at the cross section of the toner, and the largest length of the domain of the polypropylene in the major axis direction and the average distance of the space between the domains are specified. JP O.P.I. No. 10-161338 discloses one having the domain-matrix structure in which the domain diameter of the mold-releasing agent before the heat fixation is specified and the domain-matrix structure is disappeared after the fixation.
However, a cleaning mechanism is necessary even when the mold-releasing agent is introduced in the reason of that an off-set phenomenon so called as a invisible off-set is caused by accumulation of the toner onto the fixing roller after a lot of image forming operations such as a number of ten thousands to twenty thousands even though the off-set is not occurred when several copies are made. The cleaning member of the fixing device should be changed every several ten thousands times of copying.
Besides, a high speed machine capable of outputting 50 or more sheets per minute is appeared on the market accompanied with rising of the processing ability of the image forming machine. In such the machine, the mold-releasing agent contained in the toner cannot sufficiently functions since the fixing process is finished before sufficient penetration of the mold-releasing agent to the toner surface. Thus the invisible off-set is easily occurred and the off-set occurred at a stage after a little number of copying.
Moreover, the toners disclosed in the above publications are produced by a crushing method with a kneading process, and the domain of the mold-releasing agent is oriented in one direction, so called orientation, in the toner particle in the course of the kneading process. When the mold-releasing agent is oriented in the toner, the effect of the mold-releasing agent between the fixing roller and the image receiving paper is difficultly appeared since the penetration of the mold-releasing agent in all directions cannot be occurred because the penetrating direction of the mold-releasing agent is decided according to the oriented direction thereof. As mentioned above, any toner usable in the high speed machine can not be obtained by the crushing method.
The effort to make smaller the toner diameter is proceeded from the view point of the rising of image quality, and the improvement of the compound for mold-releasing agent and a technique for increasing the adding amount of the mold-releasing agent into the toner have been studied as is shown in JP O.P.I. No. 8-41468. However, problems such as the mold-releasing agent released from the toner causes degradation of the developer, lowering of the fluidity of the toner and occurrence of the filming by the reason of the structure of the toner that the toner particle is composed of a resin particle and a mold-releasing agent particle.
JP O.P.I. No. 5-88409 discloses a toner particle having a specified structure. The disclosed toner is a polymerized toner having a large spherical domain of the mold-releasing agent in a binder resin. However, a particle containing no domain of the mold-releasing agent is found in such the toner since the problem of the partial distribution of the amount of the mold-releasing agent in each of the individual particle is not solved. Moreover, degradation of the toner such as lowering of the charging ability is caused by the mold-releasing agent released from the toner particle because the contacting area between the mold-releasing agent and the resin is decreased since the shape of the mold-releasing agent in the toner particle has a spherical shape.
The toners described in the above publications have a problem that the layer of the mold-releasing agent between the fixing roller and the toner cannot be sufficiently formed since a time is necessary for penetrating out the mold-releasing agent until the toner surface because only one or two large domains of the mold-releasing agent is existed near the center of the toner particle. As above-mentioned, development of a toner suitably used in the high speed image forming machine is desired.
The first object of the invention is to provide a toner for developing a static image, which is excellent in the resistivity against the invisible off-set and forms no image contamination even when the total number of the processed image is increased accompanied with the prolongation of the using period.
The second object of the invention is to provide a toner for developing a static image excellent in the fusibility and the fluidity, in which the penetration of the mold-releasing agent to the toner surface is effectively performed so that the wind-jamming in the fixing process caused by the shortage of the mold-releasing agent is not occurred.
The third object of the invention is to provide a toner for developing a static image having a high durability in which the mold-releasing agent is not released from the toner.
The fourth object of the invention is to provide a toner for developing a static image usable for a high speed image forming apparatus having a fixing process without oiling/cleaning.
The fifth object of the invention is to provide an image forming method using the foregoing toner.
The inventors noticed on the structure of the polymerized toner having the domain-matrix structure obtained by association of a resin particle according to the invention and a particle of a crystalline substance, and found that the objects of the invention can be attained by specifying the shape and the dispersed state of the crystalline substance in the toner particle. Namely, in the invention, it is found that the objects of the invention is attained by that the shape of the crystalline substance in the toner particle is made to elliptical and the elliptical shaped crystalline substance is randomly dispersed without orientation.
In the invention, it is found that the wax is uniformly and suitably penetrated out from the toner even if the toner particle is pressed from any direction at the time of the fixing, when the crystalline substance forming the domain is suitably dispersed in the three dimensional arrangement without uneven distribution in the toner particle having the domain-matrix structure. Thus the effects such as the off-set prevention are realized.
In the invention, the toner particle is prepared in any portion of which the domain is equally dispersed, besides a toner including a portion at which the domains are densely dispersed in a state having a extremely small distance between the domains and another portion at which the domains are sparsely dispersed is not formed. The present invention and its embodiments are described below.
A toner for developing a static image comprising at least a resin, colorant and a crystalline substance, wherein the toner particle has a domain-matrix structure and the domain has an average of the ratio of the major axis to the minor axis of from 1.15 to 2.5 when the domain is approximated by an ellipse.
A toner for developing a static image comprising at least a resin, colorant and a crystalline substance, wherein the toner particle has a domain-matrix structure and the distribution of the angle of the major axis of the ellipse with the X axis optionally set on the electron microscopic photograph has two or more peaks when the domain is approximated by an ellipse.
A toner for developing a static image comprising at least a resin, colorant and a crystalline substance, wherein the toner particle has a domain-matrix structure and the distribution of the angle of the major axis of the ellipse with the X axis optionally set on the electron microscopic photograph has no peak when the domain is approximated by an ellipse.
The toner for developing a static image comprising at least a resin, colorant and a crystalline substance, wherein the toner particle has a domain-matrix structure and the domains are different in the luminance.
The toner described above, wherein the toner particle has a domain-matrix structure comprising a matrix of the resin, the domain of the colorant and an domain of the crystalline substance.
The toner described above, wherein the toner particle has a domain-matrix structure and an extract solution of the crystalline substance has a spectral transmittance of from 70.0 to 99.5%.
The toner described above, wherein the ratio of the particles having no corner is not less than 50% in number and a number variation coefficient in the particle size distribution in number is not more than 27%.
The toner described above, wherein the ratio of the toner particles having a shape coefficient of from 1.2 to 1.6 is not less than 65% in number and a number variation coefficient in the particle size distribution in number is not more than 27%.
The toner described above, wherein the toner has a number average particle diameter of from 3 to 9 xcexcm.
The toner described above, wherein the sum M of a relative frequency m1 of the toner particles contained in the highest frequency class and a relative frequency m2 of the toner particle contained in the next high frequency class in a histogram of the particle size distribution in number is not less than 70%, in the histogram, natural logarithm of log D of the diameter of the toner particle D is graduated on the horizontal axis and toner particle size is classified by every 0.23 on the horizontal axis.
The toner described above, wherein the toner particle is produced by polymerizing at least a polymerizable monomer in an aqueous medium.
The toner described above, wherein the toner particle is produced by coagulating and melt-adhering particles of the resin.
The toner described above, wherein the toner is produced by salting/melt-adhering a colorant particle and a combined fine particle of a resin prepared by dissolving the crystalline compound in a polymerizable monomer and then polymerizing the polymerizable monomer.
The toner described above, wherein the toner is produced by salting/melt-adhering a colorant particle and a combined fine particle of a resin prepared by a poly-step polymerization method.
The toner described above, wherein the toner is produced by adhering a resin layer by a salting/melt-adhering method on the surface of a resin particle and a colorant particle.
A method for producing a toner for developing a static image comprising at least a resin, colorant and a crystalline substance whereby the toner described in any one of the foregoing 1 through 15 is produced.
An image forming method comprising the steps of visualizing a static image formed on a photoreceptor, transferring the visualized image onto a recording medium, and fixing by heating the image, wherein the fixing is performed at a line speed of from 230 to 900 mm/sec, and the visualization is performed by the use of the toner described above.
The image forming method described above which comprises the steps of
visualizing a static image formed on a photoreceptor,
transferring the visualized image onto a recording medium, and, fixing by heating the image, wherein light exposed to the photoreceptor is performed by digitalized exposure.
A toner described above, wherein the DSC curve of the toner has an endothermic peak within the range of from 60 to 110xc2x0 C. and an endotherm quantity of from 4 to 30 j/g, the toner particle has a domain-matrix structure in which the average of the smallest distance between the walls of the domains is from 100 to 1060 nm, and domains each has the smallest distance between the wall of the neighbor domain of not less than 1300 nm account for not more than 10% in number of the whole domains.
A toner described above wherein the DSC curve of the toner has an endothermic peak within the range of from 60 to 110xc2x0 C. and an endotherm quantity of from 4 to 30 j/g, the toner particle has a domain-matrix structure in which the average of the smallest distance between the walls of the domains is from 260 to 820 nm, and domains each has the smallest distance between the wall of the neighbor domain of not less than 1300 nm account for not more than 4% in number of the whole domains.
A toner described above wherein the toner particle has a domain-matrix structure and the number of the domain exposed at the surface of the toner particle is zero.
A toner described above wherein the toner particle has a domain-matrix structure, and the average area of Voronoi polygons each formed by lines each perpendicularly and equally dividing the line connecting between the gravity centers of the neighbor domains is from 20,000 to 120,000 nm2 and the variation coefficient of the area of the Voronoi polygon is not more than 25%.
A toner described above wherein the toner particle has a domain-matrix structure, and the average area of Voronoi polygons each formed by lines each perpendicularly and equally dividing the line connecting between the gravity centers of the neighbor domains is from 40,000 to 100,000 nm2 and the variation coefficient of the area of the Voronoi polygon is not more than 20%.
A toner described above wherein the toner particle has a domain-matrix structure, and the average area of Voronoi polygons each formed by lines each perpendicularly and equally dividing the line connecting between the gravity centers of the neighbor domains is from 20,000 to 120,000 nm2, and the domains each having the Voronoi polygon having an area of not less than 160,000 nm2 account for from 3 to 20% in number.
A toner described above wherein the toner particle has a domain-matrix structure, and the average area of Voronoi polygons each formed by lines each perpendicularly and equally dividing the line connecting between the gravity centers of the neighbor domains existing outside of a circle having radius of 1,000 nm and the center at the gravity center of the cross section of the toner particle is larger than the average area of Voronoi polygons each formed by lines each perpendicularly and equally dividing the line connecting between the gravity centers of the neighbor domains existing inside the circle.
A toner described above wherein among Voronoi polygons each formed by lines each perpendicularly and equally dividing the line connecting between the gravity centers of the neighbor domains, exist from 5 to 30 domains having the Voronoi polygon which contact with the outside of the toner particle and has an area of not less than 160,000 nm2.
A toner described above wherein the domains include domains different in the luminance from each other.
A toner described above wherein the matrix is constituted by the resin and the domains constituted by the domain of the crystalline substance and the domain of the colorant.